This invention relates generally to an electrophotographic printing machine, and more particularly concerns a cover for holding an original document onto the printing machine platen during the reproduction process.
In electrophotographic printing, a photoconductive member is uniformly charged and exposed to a light image of an original document. This records on the photoconductive surface an electrostatic latent image corresponding to the original document. The electrostatic latent image is developed by depositing toner particles thereon in image configuration. Thereafter, the toner powder image is transferred to a sheet of support material and permanently affixed thereto providing a copy of the original document. The foregoing process was originally disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.
Multi-color electrophotographic printing is substantially the same as the foregoing process with the additional requirement that a plurality of single color images are formed. Each single color light image is developed with toner particles complementary in color thereto. The differently colored toner powder images are transferred, in superimposed registration with one another, to the sheet of support material. This multi-layered powder image is then permanently affixed to the sheet of support material forming a color copy of the original document.
With the advent of high quality multi-color electrophotographic printing, exposure system requires greater light intensity than as heretofore necessary.
An exposure system of this type may generate light rays which are hazardous to the retina of the human eye. Attempts to overcome this problem by preventing light leakage are described in U.S. Pat. Nos. 3,642,371 and 3,642,376. In the foregoing patents, the platen cover has a top housing with an open bottom overlying the platen glass on which the original document being reproduced is positioned. A flexible diaphragm is secured to the bottom of the top housing to form a light-tight covering of the platen glass to prevent the escape of light rays therefrom. Systems of this type have not proven to be entirely satisfactory when light rays of the intensity required a milti-color electrophotographic printing are employed.
Accordingly, it is a primary object of the present invention to improve the platen cover employed in an electrophotographic printing machine.